Slaanesh slew most of the Eldar and their Gods in the Immaterium, except for the Eldar God of War Kaela Mensha Khaine, whose energy was dispersed into many separate pieces scattered across the various Infinity Circuits of the Eldar Craftworlds, the Laughing God Cegorach, who fled into the Labyrinthine Dimension of the Webway, and while Isha was defeated, she was not destroyed outright and absorbed by Slaanesh like the rest of the Eldar Pantheon after his birth during the Fall of the Eldar.
Slaanesh vanquished her as he had all of the other Eldar Gods within the Warp, but only took her prisoner rather than absorbing her energies outright.
Other Eldar survivors included the Harlequin, and those Craftworld Eldar who were very far away from the Eldar homeworlds when the Warp rift formed.
Most of the survivors that remain have become sworn enemies of the Dark Prince, and yet a few of them have formed isolated cabals that still behave as their ancestors did, perversely following the downward spiral of excess.
Over several generations, this indolence came to rule and pervert their spirits.
In the Immaterium, the collective psychic reflections of their indolence and hedonism caused a new Chaos Power to stir, beginning in the 25th Millennium of the Terran calendar.
Instead, they were able to dedicate their lives to whatever idle pursuits took their fancy.The Fall of the Eldar in the early 30th Millennium was signalled by the birth-scream of Slaanesh, a tsunami of emotion that heralded the Prince of Pleasure arrival in the Realm of Chaos.The psychic implosion caused by Slaanesh's birth swallowed hundreds of worlds at the heart of the Eldar empire in what is now the Imperium of Man's Segmentum Obscurus, killing billions of Eldar in a single instant and devouring a great section of the galaxy in the process.In turn, as Slaanesh grew, its nascent dreams trickled into the minds of the Eldar and fuelled their desires, pushing them ever onwards towards their eventual doom.Eventually, the Eldar civilisation devolved into little more than pleasure cults dedicated to every act of physical, mental and spiritual fulfillment.